diff --git a/l4d2web/tests/e2e/test_files_overlay.py b/l4d2web/tests/e2e/test_files_overlay.py
index e9752df..a1ee693 100644
--- a/l4d2web/tests/e2e/test_files_overlay.py
+++ b/l4d2web/tests/e2e/test_files_overlay.py
@@ -14,6 +14,8 @@ docs/superpowers/plans/2026-05-17-files-overlay-e2e-handoff.md.
 """
 from __future__ import annotations
 
+import urllib.parse
+
 import pytest
 from playwright.sync_api import Page, expect
 
@@ -383,3 +385,30 @@ def test_filename_rename_on_save(page: Page, files_overlay_server) -> None:
     expect(
         page.locator('.file-tree-row-file[data-target-path="server.cfg"]')
     ).to_have_count(0)
+
+
+def test_share_url_deep_link_reopens_editor(page: Page, files_overlay_server) -> None:
+    """Navigate directly to /overlays/<id>?modal=<urlencoded edit path>
+    and assert the routed editor auto-opens for the right file. This
+    is the central guarantee of the URL-addressable modals spec — copy
+    the current URL, paste it in a new tab (or share it), and the
+    modal reopens. Without this test, a regression in modals.js's
+    DOMContentLoaded bootstrap (the `URLSearchParams.get("modal") →
+    fetchAndShowRouted` chain) would silently make every shared link
+    dead.
+
+    The `?modal=` param holds the UNENCODED routed path; URLSearchParams
+    decodes it for us. We pass the URL-encoded version through quote()
+    so the surrounding URL stays valid.
+    """
+    base = files_overlay_server["base_url"]
+    overlay_id = files_overlay_server["overlay_id"]
+
+    login(page, base)
+    modal_path = f"/overlays/{overlay_id}/files/edit?path=server.cfg"
+    page.goto(
+        f"{base}/overlays/{overlay_id}?modal={urllib.parse.quote(modal_path)}"
+    )
+
+    _wait_for_routed_editor(page)
+    assert page.locator('textarea[data-rel-path="server.cfg"]').count() == 1